(Disclaimer: as a writer, I do understand that “apocalypse”
is actually a revelation, but for this article I will adopt its common
meaning of an all-encompassing disaster.)

Many classic fantasy tales have a post-apocalyptic element.
Of course, as for most Western-based fantasy tropes, Tolkien is the
standard-setter. (Tolkien’s ages of Middle-Earth parallel Greek
mythology, which named the four Ages of Man: Golden, Silver, Bronze, and
Iron. I’m guessing, given his background, that this was deliberate.)
The backdrop for Lord of the Rings includes two former ages, each
ended by their own apocalypse. The end of the First (Golden) Age, when
Morgoth was defeated, was accompanied by great destruction—it was said
the lands were broken, and Beleriand began to sink into the sea. The
Second (Silver) Age ended with Númenor sinking into the sea, and the
formerly flat world being made round.

But there are sudden disasters and slow declines, and Tolkien wove both
into Middle-Earth history. During the Third (Bronze) Age, Men and Elves
joined forces to defeat Sauron, achieving a Pyrrhic victory. From the
end of the war, to the end of the Third Age, Middle-Earth saw a gradual
and general decline. Gondor was diminished over the ensuing centuries,
losing its King and population. (In this time, the old folks were right
when they said things used to be better.) Elves also declined in
population, as many opted to withdraw from the affairs of Middle-Earth
and seek the peace of the Undying Lands. Worse, Sauron’s ring was not
destroyed, and then was lost… and that led to the events depicted in The Hobbit and Lord of the Rings.

In homage to Tolkien, many fantasy worlds often include an
apocalypse as an echo from a distant past. The dark age that followed is
ending or ended, and at least some recovery has taken place—all the
better to set up the primary conflict, by threatening what has been
regained. Such conflict is a staple of epic fantasy: a looming disaster,
often unfinished business from the ancient past, sets the main
characters on their quest to save the world.

My own post-apocalyptic writing, both paranormal and
fantasy, pits humanity against an enemy more implacable than Sauron or
even Morgoth: nature itself. In my own fantasy world of Termag, a
pandemic calamity known only as The Madness destroyed Camac That Was. In
the ensuing four centuries, known as the Lost Years, the remnants of
the empire attempted to save what was left, or at least re-establish
order. The ensuing Age of Heroes established a new civilization, or set
of civilizations, with some vestiges of the old order. While my Accidental Sorcerers series takes place after the Age of Heroes, my novella The Crossover is set near the end of the Age of Heroes, and is free at Amazon and other eBook outlets at least for a while longer.

I’m sure that most people consider “post-apocalyptic”
stories to be those set immediately after the apocalypse in question,
but the word “after” doesn’t specify a timeframe. Still, it might be
interesting to read (or write) a fantasy story that happens just after
an apocalypse. I’ll have to explore The Lost Years some time…